The electrical resistivity of a metallic conductor decreases gradually as the temperature is lowered. However, in ordinary conductors such as copper and silver, this decrease is limited by impurities and other defects. Even near absolute zero, a real sample of copper shows some resistance. Despite these imperfections, in a superconductor the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source.[1]

In 1986, it was discovered that some cuprate-perovskiteceramic materials have critical temperatures above 90 K (−183 °C). These high-temperature superconductors renewed interest in the topic because of the prospects for improvement and potential room-temperature superconductivity. From a practical perspective, even 90 kelvins is relatively easy to reach with the readily available liquid nitrogen (boiling point 77 kelvins), resulting in more experiments and applications.